In order to collect information on the volume of traffic or acquire information used to control the switching of a traffic signal, a technology for measuring the length of a queue of vehicles that temporarily stop (hereinafter, simply referred to as “vehicle queue length”) has been studied. See, for example, Japanese Laid-Open Patent Publication Nos. 2010-44525, 2003-346278 and 2007-141179.
For example, in a technology disclosed in Japanese Laid-Open Patent Publication No. 2010-44525, probe information acquired from a probe car is used to specify a time when the probe car passes through a vehicle detector's detection area, a time when the probe vehicle reaches the end of a vehicle queue waiting for a traffic signal, and a position that the probe vehicle reaches. The specified information, such as the time when the probe vehicle passes through the vehicle detector's detection area, the time when the probe vehicle reaches the end of the queue waiting for the traffic signal, and the position reached, are used to calculate a position of a vehicle when the vehicle having passed through the detection area reaches the end of the vehicle queue waiting at the traffic signal at a given time.
Further, Japanese Laid-Open Patent Publication No. 2003-346278 discloses a technology for measuring vehicle queue length by installing a camera so that the lens of the camera faces the same direction as the travelling direction of a vehicle and photographing an image of the road from a position behind the vehicle.
In addition, Japanese Laid-Open Patent Publication No. 2007-141179 discloses a technology where, when a brake is operated, a braking distance is obtained after obtaining an average deceleration of a vehicle to obtain a reaching position where the vehicle stops on the basis of the braking distance.